merge1(int low, int high, int S[], U[]) 
{ 
     int k = (high - low + 1)/2
     for q (from low to high) U[q] = S[q]
     int j = low 
     int p = low 
     int i = low + k 

     while (j <= low + k - 1) and (i <= high) do 
  { 
           if ( U[j] <= U[i] ) 
           {
        S[p] := U[j] 
        j := j+1
        } 
       else 
          { 
             S[p] := U[i] 
          i := i+1 
       } 
       p := p+1 
  } 

 if (j <= low + k - 1) 
 { 
     for q from p to high do 
     { 
      S[q] := U[j] 
      j := j+1 
     } 
 }
}


merge_sort1(int low, int high, int S[], U[]) 
{ 
  if low < high 
  { 
     int k := (high - low + 1)/2 

merge_sort1(low, low+k-1, S, U) merge_sort1(low+k, high, S, U) merge1(low, high, S, U) } }

I am really sorry for the terrible formating, as you can tell I am not a regular visitor here.

So, basically, this is on my lecture notes. I find it quite confusing in general but I understand the biggest part of it. What I don't understand is the need of the "if (j <= low + k - 1)" part. It looks like it checks if there are any elements "left" in the left part. Is that even possible when mergesorting?